A phenomenon that atoms or molecules are ejected from a target by a high-speed bombardment of an inert substance such as Ar, etc. is called “sputtering.” The ejected atoms or molecules can be accumulated on a substrate to form a thin film. A magnetron sputtering method uses a magnetic field in a cathode to increase a speed of accumulating a target material on a substrate, and can form a film at low temperatures because electrons do not impinge on substrates. Accordingly, the magnetron sputtering method is widely used to produce electronic parts such as semiconductor ICs, flat panel displays, solar cells, etc., and to form thin films such as reflection films, etc. on substrate surfaces.
A magnetron sputtering apparatus comprises a substrate on the anode side, a target (cathode) arranged to oppose the substrate, and a magnetic-field-generating apparatus arranged below the target, in a vacuum chamber. With voltage applied between the anode and the cathode to cause glow discharge for ionizing an inert gas (Ar at about 0.1 Pa, etc.) in the vacuum chamber, secondary electrons discharged from the target are captured by a magnetic field generated by the magnetic-field-generating apparatus, causing a cyclotron motion on a target surface. Because the cyclotron motion of electrons accelerates the ionization of gas molecules, a film-forming speed is dramatically higher than when a magnetic field is not used, resulting in strong adhesion of a film.
As shown in FIG. 21, a magnetic circuit apparatus 150 used in a magnetron sputtering apparatus comprises a plate- or rod-shaped, center magnet 160 magnetized in a height direction (perpendicular to a target surface), a peripheral rectangular magnet 170 magnetized in an opposite direction to the center magnet 160 and arranged around the center magnet 160, and a yoke 180 supporting the center magnet 160 and the peripheral magnet 170, to generate a magnetic field in a racetrack form on a target surface (for example, see JP 8-134640 A). With a racetrack-shaped magnetic circuit, secondary electrons can be contained in a closed space, resulting in a high sputtering efficiency. To form a closed space for containing secondary electrons, a magnetic field of 10 mT or more as a horizontal component of a magnetic flux density is usually needed.
The erosion of a target is fastest in a portion shown by a broken line 190 in FIG. 22, in which a vertical component of a magnetic flux density is zero in the magnetic circuit. Accordingly, the magnetic field on a target surface should be adjusted, such that erosion in a portion in which a magnetic flux density has no vertical component, which is simply called “vertical-component-free magnetic flux density portion,” is as close to erosion in other portions as possible. However, because the distance of a vertical-component-free magnetic flux density portion 190 from the center magnet 160 is larger in the linear portion of the magnetic circuit (distance R) than in the corner portions (distance r) (r<R), in the magnetic circuit apparatus 150 as shown in FIG. 21, magnetic flux is concentrated in the vertical-component-free magnetic flux density portion in the corner portions. As a result, plasma is concentrated in the corner portions, resulting in the fastest erosion in the corner portions. Though JP 8-134640 A discloses a technology of arranging magnets in a T form in the corner portions to eliminate the unevenness of a vertical magnetic flux density in the corner portions, its improvement is not sufficient.
JP 2008-156735 A discloses, as shown in FIG. 23(a) and FIG. 23(b), a magnetic-field-generating apparatus 200 for magnetron sputtering, which comprises a non-magnetic base 210, a rod-shaped center magnetic pole piece 220 disposed on the non-magnetic base 210, a peripheral racetrack-shaped magnetic pole piece 230 disposed around the center magnetic pole piece 220, and plural permanent magnets 240, 250 arranged between the center magnetic pole piece 220 and the peripheral magnetic pole piece 230, the permanent magnets 240, 250 being magnetized in a horizontal direction and arranged with their magnetic poles of the same polarity opposing the center magnetic pole piece 220, and the center magnetic pole piece 220 and the peripheral magnetic pole piece 230 being higher than the permanent magnets 240, 250. Because magnetic pole surfaces of the permanent magnets 240, 250 are in contact with the magnetic pole pieces 220, 230 in this magnetic-field-generating apparatus, the leakage of magnetic flux from the permanent magnets 240, 250 is reduced, resulting in a larger region than ever, in which a magnetic field intensity (having a horizontal magnetic flux density of 10 mT or more) necessary for containing a plasma-excited inert gas with a smaller number of permanent magnets is obtained. As a result, the erosion region of a target is expanded, resulting in more uniform erosion in the linear and corner portions of the magnetic circuit.
Though the erosion region of a target in corner portions is wider in the magnetic-field-generating apparatus of JP 2008-156735 A than in that of JP 8-134640 A, there is less erosion near the center magnetic pole piece 220 because the deepest erosion portion in the linear portion is close to the peripheral magnetic pole piece 230. Thus, it has been found that an erosion region should also be expanded in a center portion of the magnetic-field-generating apparatus.
JP 1-147063 A discloses, as shown in FIGS. 26(a) and 26(b), a circular magnetic-field-generating apparatus for magnetron sputtering, which comprises concentric magnetic shunt plates 311a, 311b, 311c above a magnetic circuit comprising concentric magnets 302a, 302b, 303. A portion having a strong horizontal magnetic field is expanded and made more uniform by the magnetic shunt plates 311a, 311b, 311c, resulting in more uniform erosion of the target. However, the shunt plates cannot sufficiently expand a magnetic flux density distribution near the center magnetic pole piece in a magnetic-field-generating apparatus for magnetron sputtering with the magnetization direction of magnets in parallel to the target as described in JP 2008-156735 A, though the shunt plates are effective for a magnetic-field-generating apparatus for magnetron sputtering with the magnetization direction of magnets perpendicular to the target.
JP 2009-108383 A discloses, as shown in FIG. 27, a target apparatus for magnetron sputtering using a cylindrical or planar target, which comprises a magnet unit comprising magnets 324b, 324c arranged in a zigzag manner on a support member 324a to generate a magnetic field inclined relative to the longitudinal direction of the target. However, it is difficult to produce this magnet unit because of the complicated arrangement of magnets 324b, 324c. 